How to redirect cin and cout to files

Question

How can I redirect cin to in txt and cout to out txt

User · Answer

Just write   include  lt cstdio gt   include  lt iostream gt  using namespace std   int main         freopen  output txt   w  stdout       cout lt  lt  write in file       return 0

User · Answer

If your input file is in txt  you can use freopen to set stdin file as in txt freopen  quot in txt quot   quot r quot  stdin    if you want to do the same with your output  freopen  quot out txt quot   quot w quot  stdout    this will work for std  cin  if using c     printf  etc    This will also help you in debugging your code in clion  vscode

User · Answer

assuming your compiles prog name is x exe  and   is the  system shell or prompt     x  lt infile  gt outfile    will take input from infile and will output to outfile

User · Answer

Try this to redirect cout to file    include  lt iostream gt   include  lt fstream gt   int main             backup cout buffer and redirect to out txt         std  ofstream out  out txt         auto  coutbuf   std  cout rdbuf        std  cout rdbuf out rdbuf          std  cout  lt  lt   This will be redirected to file out txt   lt  lt  std  endl           reset cout buffer         std  cout rdbuf coutbuf        std  cout  lt  lt   This will be printed on console   lt  lt  std  endl       return 0      Read full article Use std  rdbuf to Redirect cin and cout

User · Answer

Here is an working example of what you want to do  Read the comments to know what each line in the code does  I ve tested it on my pc with gcc 4 6 1  it works fine    include  lt iostream gt   include  lt fstream gt   include  lt string gt   void f         std  string line      while std  getline std  cin  line      input from the file in txt               std  cout  lt  lt  line  lt  lt    n       output to the file out txt         int main         std  ifstream in  in txt        std  streambuf  cinbuf   std  cin rdbuf      save old buf     std  cin rdbuf in rdbuf       redirect std  cin to in txt       std  ofstream out  out txt        std  streambuf  coutbuf   std  cout rdbuf      save old buf     std  cout rdbuf out rdbuf       redirect std  cout to out txt       std  string word      std  cin  gt  gt  word              input from the file in txt     std  cout  lt  lt  word  lt  lt           output to the file out txt      f      call function       std  cin rdbuf cinbuf       reset to standard input again     std  cout rdbuf coutbuf     reset to standard output again      std  cin  gt  gt  word      input from the standard input     std  cout  lt  lt  word     output to the standard input     You could save and redirect in just one line as   auto cinbuf   std  cin rdbuf in rdbuf       save and redirect   Here std  cin rdbuf in rdbuf    sets std  cin s buffer to in rdbuf   and then returns the old buffer associated with std  cin  The very same can be done with std  cout  mdash  or any stream for that matter   Hope that helps

User · Answer

Here is a short code snippet for shadowing cin cout useful for programming contests    include  lt bits stdc   h gt   using namespace std   int main         ifstream cin  input txt        ofstream cout  output txt         int a  b         cin  gt  gt  a  gt  gt  b      cout  lt  lt  a   b  lt  lt  endl      This gives additional benefit that plain fstreams are faster than synced stdio streams  But this works only for the scope of single function   Global cin cout redirect can be written as    include  lt bits stdc   h gt   using namespace std   void func         int a  b      std  cin  gt  gt  a  gt  gt  b      std  cout  lt  lt  a   b  lt  lt  endl     int main         ifstream cin  input txt        ofstream cout  output txt            optional performance optimizations         ios base  sync with stdio false       std  cin tie 0        std  cin rdbuf cin rdbuf         std  cout rdbuf cout rdbuf          func        Note that ios base  sync with stdio also resets std  cin rdbuf  So the order matters   See also Significance of ios base  sync with stdio false   cin tie NULL    Std io streams can also be easily shadowed for the scope of single file  which is useful for competitive programming    include  lt bits stdc   h gt   using std  endl   std  ifstream cin  input txt    std  ofstream cout  output txt     int a  b   void read         cin  gt  gt  a  gt  gt  b     void write         cout  lt  lt  a   b  lt  lt  endl     int main         read        write        But in this case we have to pick std declarations one by one and avoid using namespace std  as it would give ambiguity error   error  reference to  cin  is ambiguous      cin  gt  gt  a  gt  gt  b         note  candidates are   std  ifstream cin     ifstream cin  input txt                       In file test cpp std  istream std  cin     extern istream cin       Linked to standard input                        See also How do you properly use namespaces in C     Why is  quot using namespace std quot  considered bad practice  and How to resolve a name collision between a C   namespace and a global function

[c++] How to redirect cin and cout to files?

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